If you would like to learn to juggle, start by buying some bean bags to practise with as they are slower and heavier to throw and catch than balls and it help to master the juggling process. Once you have worked out how to throw and catch the bean bags, you can get a set of soft juggling balls that are fairly heavy. If you want to make your own you can get balloons and fill them with rice, but best to use a double layer of balloons so that they don't split too easily. Juggling balls come in a range of different prices. If you're just starting out, you don't need to spend too much, but on the other hand, the slightly more expensive balls are squashier, so easier to throw and catch.
To begin, practise with one ball, throwing and catching. Then move on to throwing two balls against a wall. Throw the first ball so it hits the wall at eye level and as the ball rebounds towards you, release the second ball so you can catch the first. Get a good rhythm going. Once you have worked this out, you can introduce the third ball.
To juggle with three balls, put two balls into either hand and one in your other hand. Imagine a triangle in the air where both hands are the bottom two points of the triangle and the top angle is level with your eyes. Throw one of the balls in the hand where you are holding two. Keep your eyes on the imaginary top angle of the triangle. As the first ball reaches the top point, throw the single ball from your other hand and aim that for the same point, as the first ball falls into your empty hand. Catch the first ball and throw the third ball from your other hand towards the top angle and catch the second ball in your empty hand. Practise developing the rhythm and adopt a nice relaxed stance with your feet slightly apart. Try not to move your legs or feet as this will affect your balance. Remember to have a ball in each hand and one at the top-point level with your eyes at all times, and keep your eyes on the top point.